The present invention relates to devices used for reducing noise emissions in turbocharger systems, and more specifically, to a compressor inlet configuration that is used to reduce noise in a turbocharger.
The use of turbochargers to increase the intake air pressure of internal combustion engines is a common, well known means to increase engine output. A turbocharger system typically comprises a turbine wheel and a compressor wheel, often mounted on a common shaft, and disposed within respective housings of the turbocharger. The exhaust generated by an internal combustion engine is routed to the turbine, where the exhaust is used to drive a turbine wheel. The turbine wheel is generally an impeller, having blades or vanes. The turbine wheel turns a shaft, which is coupled, directly or indirectly, to a compressor wheel, that is also generally a bladed impeller type of wheel. The compressor wheel draws in intake air, compresses it, and supplies the air to the internal combustion engine. In many conventional turbochargers the compressor wheel is driven at high speeds or revolutions per minute. Many turbine wheels (and thus compressor wheels) rotate at a speed in the range of 100,000 to 150,000 revolutions per minute. This high speed rotation of the turbine and compressor wheels causes the turbine and compressor blades to generate high levels of noise, known as Blade Pass Frequency noise, or sometimes informally referred to as turbo whine.
To increase the performance of compressors in such systems, a bypass port is often added to the main compressor inlet, typically utilizing a ported shroud configuration. While a typical compressor generally has a single inlet to the compressor wheel, defined by the housing of the compressor, the ported shroud or bypass port provides an inlet with inner and outer portions. Typically, a ported shroud compressor has a housing similar to previously known compressors, with the housing defining a compressor inlet and outlet, but also having an additional wall. In a typical bypass port configuration such as the ported shroud, the compressor wheel is mounted in a central portion of the compressor housing, defined by an additional cylindrical inner wall inside the compressor housing which forms a shroud within the outer wall of the compressor housing. This inner wall extends beyond the compressor wheel, but does not extend as far outward as the housing of the compressor. An outer portion of the inlet is defined within the compressor housing, extending inward from the end of the housing to the end of the cylindrical inner wall. At that point, the outer portion of the inlet is adjacent to the inner portion of the inlet. The inner portion of the inlet has a central channel, defined within the inner surface of the inner wall or shroud, and providing a path to the face of the compressor wheel. The inner portion of the inlet also has an annular channel defined between the inner surface of the compressor housing and the outer surface of the inner wall (the shroud). The annular channel runs from the outer portion of the inlet to the vanes or blades of the compressor wheel.
The addition of a bypass port increases the operating range of a compressor. Typically, a compressor""s operating range is limited at low speeds by a phenomena referred to in the industry as xe2x80x9csurge,xe2x80x9d where the volume of air provided to the compressor exceeds the system""s requirements, and limited at high speeds by a phenomena referred to in the industry as xe2x80x9cchoke,xe2x80x9d where the system""s air requirements exceed the compressor""s maximum flow rate. The annular channel, or port, in communication with the compressor wheel acts as a bypass. At low speeds, which might otherwise cause a surge condition, the port allows flowback from the compressor wheel to the main inlet, allowing the system to reach equilibrium. At high speeds, which might otherwise cause a choke condition, the port allows extra air to be drawn directly into the blades of the compressor wheel. Compressors configured with this type of inlet are sometimes known as xe2x80x9cmap width enhancedxe2x80x9d compressors.
However, the performance improvements of this type of compressor come at the cost of increased noise. The port, or bypass, provides a direct path to the compressor wheel, and thus provides a means for the noise (sound waves) generated by the high speed revolutions of the compressor wheel to exit the compressor housing. One method of addressing this situation is by placing baffles along the annular channel, creating a xe2x80x9ctorturousxe2x80x9d path for the air and sound waves to traverse. Another method used has been to insert a conical baffle in the outer portion of the inlet of the compressor. Although these methods provide some measure of noise reduction, further noise reduction is required, and at a lower cost. Thus, there exists the need for an economical device to reduce noise transmission from a shrouded compressor, and which may be used in a range of shrouded compressor configurations.
The present invention provides an economical device for reducing noise emissions from a turbocharger bypass port compressor. The device comprises an annular inner deflector for attachment in the first portion of the inlet of a ported shroud compressor. A secondary noise suppressor may also be used in conjunction with the inner deflector to further reduce noise transmission.
The inner deflector is a ring-shaped device with several noise blocking surfaces. A simple approximation of its shape would be to take a circle and extrude it over a xe2x80x9cJxe2x80x9d or xe2x80x9cLxe2x80x9d shaped path. A first surface is substantially parallel to the walls and flow of the bypass port, and provides the point of attachment to a wall of the bypass port. A second surface is substantially perpendicular to the first surface, and substantially perpendicular to the flow within the bypass port. This second surface prevents unobstructed flow of noise through the bypass by blocking the linear or xe2x80x9cline of sightxe2x80x9d flow of sound waves. A third surface, substantially parallel to the first surface and the walls of the bypass port, and substantially perpendicular to the second surface, acts to further contain sound waves, and to dampen the intensity of the waves, thus further reducing noise transmission. The planar blocking surfaces disrupt xe2x80x9cline of sightxe2x80x9d transmission of sound waves from the compressor wheel, forcing the sound waves to travel a longer path, losing some energy along the way. In addition, some noise reduction occurs due to the canceling effects of sound waves colliding along the path defined by the inner wall and the inner deflector. The positioning of the inner deflector, as well as the lengths of the various surfaces of the inner deflector, are dependant on the type of application, and may be varied to achieve maximum noise reduction, considering all factors such as frequency, reflection, resonance, and cancellation of the sound waves.
A secondary noise suppressor ring further reduces noise transmission by increasing the length of the path that the sound waves must travel to escape the compressor, thus experiencing attenuation of the sound wave.
An additional advantage of the present invention is that the inner deflector no longer must be matched to the trim size of each compressor wheel, thereby reducing the cost of producing inner deflectors, and increasing the range of use for the deflector. Thus the tooling cost for reducing noise on ported shroud compressor stage turbochargers is reduced.